The present invention concerns a variable transmission which automatically changes its transmission ratio in accordance with the resistance to propagation of the vehicle and in which the power-transmitting transmission link is a V-belt or equivalent, and wherein at least the secondary pulley consists of cup disks urged against each other and interconected with a multiple-end screw and a compression spring, which at the same time is a torsion spring and is so settable adjustable in connection with assembly or adjustable that the torsion effect of the spring can increase or decrease the screw force urging the cup disks together which is caused by the moment of the peripheral force acting from the belt on the axially displaceable cup disk.
An automatic variable transmission for a bicycle is known in the art for instance through the reference DE PS 93896, the principle of the transmission therein disclosed being that the pulleys for the flat belt serving as transmission link are made of helical leaf springs which in the secondary pulley are curved in the direction of rotation and in the primary pulley, against it. this principle has later been applied in several references, for instance supplementing or replacing the springs with levers moving in helical grooves. A drawback of transmissions of this type are pulley designs which are complex and involve friction and are sensitive to dust and dirt.
A torque-sensing V-belt pulley is known in the art for instance through the reference DE PS 224180, where, to be sure, the pressure effect of the cup disk rotating with reference to the other half with screw juncture only serves to boost the lever control acting on both belt pulleys. V-belt pulleys consisting of cup disks which are non-rotatable in relation to each other have been tried out in the first place in drives for auxiliary apparatus of internal combustion engines, such as charging generators and fans, where compression or torsion springs also occur in addition to threads. A design of this kind is for instance disclosed in the reference USP 2,478,289.
The object of the present invention is to eliminate the above drawbacks. The variable transmission of the invention automatically changing transmission ratio in accordance with the resistance to propagation of the vehicle is characterized in that the torque on the shaft of the secondary belt pulley is controllable while driving with a particular cylinder which pushes the cup disks of the belt pulley apart, applying a force the stronger the higher the pressure in the cylinder. The object of the invention is to provide a variable transmission which in all circumstances automatically and steplessly changes its transmission ratio and which is competitive in efficiency with a chain transmission, and which has not been achieved so far in spite of endeavours.
An advantageous embodiment of the variable transmission of the invention in which the power-transmitting transmission link is a V-belt or equivalent and in which at least the secondary pulley consists of cup disks urged against each other and interconnected with a multiple-end screw and a compression spring is characterized in that the screw with at least three ends interconnecting the cup disks of the secondary V-belt pulley is a ball screw.
An advantageous embodiment of the variable transmission of the invetnion wherein the primary pulley is fixed is characterized in that pressure increase in the cylinder pushing the cup disks of the secondary belt pulley apart increases the tension of the V-belt with the aid of a cylinder acting on the jockey pulley.
An advantageous embodiment of the variable transmission of the invention in which also the primary pulley is adjuatable is characterized in that the same pressurized fluid which pushes apart the cup disks of the secondary pulley urges together the cup disks in the primary pulley.
An advantageous embodiment of the variable transmission of the invention for use on a bicycle is also characterized in that the pressure control means is placed on the handle-bar of the bicycle and provided with a pressure gauge.
An advantageous embodiment of the variable transmission of the invention for a motor-driven vehicle, in which the cup disks of the primary belt pulley are urged together by action of springs and of a cylinder containing pressurized fluid is also characterized in that the pressure control of the pressurized fluid has been connected to the control system of the engine.
An advantageous embodiment of the variable transmission of the invention is also characterized in that at least one surface touching the side of the belt on the pulleys transmitting power is grooved in a manner known in itself in the art.
An advantageous embodiment of the variable transmission of the invention is also characterized in that the curved shape of the grooving approximates an evolvent.
An advantageous embodiment of the variable transmission of the invention is also characterized in that in the flow passage of the pressurized fluid is provided an adjustable resistance check valve known in itself in the art, with the aid of which the movement of the cup disks of the secondary belt pulley away from each other can be retarded when the torque goes down.